Development of intestinal mucin 2, IgA, and polymeric Ig receptor expressions in broiler chickens and Pekin ducks.

Intestinal mucin 2 (MUC2), a major gel-forming mucin, represents a primary barrier component of mucus layers and a target site for secretory IgA. Polymeric Ig receptor (pIgR) expressed on the basolateral surface of epithelium is used to transport polymeric IgA from the lamina propria into luminal mucins to establish the first lines of intestinal defense. To determine the spatio-temporal expression of MUC2, IgA, and pIgR in broiler chickens and Pekin ducks, intestinal tissues (n=6/age) were dissected from late embryonic days up to 21 d posthatch. In the intestinal tissues, MUC2 was expressed with a rapid increase at hatching, followed by steady expression through 21 d posthatch both in chickens and ducks. IgA expression was low during the first week following hatching for both species. From the second week posthatch, IgA was rapidly expressed in the chickens, arriving at steady expression in the third week after hatching. However, in ducks, IgA expression during the 2 to 3 wk posthatch period was relatively slow. The expression of pIgR was greatly increased after hatching for both species, but its expression in ducks was relatively delayed. In addition, intestinal pIgR expression was highly correlated with MUC2 and IgA expressions in chickens but just moderately correlated in ducks. The relatively slow and late expression of IgA and pIgR as well as their moderate correlation may or may not account for the susceptibility of ducklings to mucosal pathogens at a young age.